1. Field of the Invention
The present invention relates to a radio-frequency (RF) matching unit, and more particularly to an RF matching unit having a variable inductor which facilitates variable control, for use in a high frequency and high power application, such as for coupling RF power to a plasma within a plasma reaction chamber of a semiconductor wafer processing system and the like.
2. Description of Related Art
A plasma enhanced semiconductor wafer processing system generally includes a plasma reaction chamber within which certain plasma enhanced processes are performed on a semiconductor wafer. To produce a plasma within the reaction chamber, a reactant gas is pumped into the chamber and a high power RF signal is coupled to the gas. The RF energy excites the reactant gas and produces a plasma within the chamber.
To uniformly maintain the plasma at a level which the plasma enhanced processes require, the RF energy has to be supplied stably to the chamber. For this purpose, an RF matching unit is used to match impedance of an RF generator to the impedance of the chamber atmosphere. However, since the impedance of the chamber atmosphere is time variant, the RF matching unit must be dynamically tuned to maintain the impedance match.
A conventional RF matching unit generally includes a variable inductor having a spiral shaped fixed coil and a plurality of rotating shield blades. Each of shielding blades is interspersed between each pair of coil turns of the fixed coil. To tune inductance of the variable inductor, the position of the shielding blades is controlled by using a position feedback technique well known in the art. However, it takes a long time for an RF match between the RF generator and the chamber to be achieved, and the variable inductor generates a large amount of heat. Also, since current flow through the fixed coil is shielded according to a rotated angle of the shielding blades, the shielding blades are apt to be heated. As a result, surfaces of the shielding blades are often oxidized to generate arcs, increasing contact resistance of contact portions of the variable inductor, thereby deteriorating RF match efficiency. Particularly, in the case that the shielding blades formed of metal material are oxidized, the time needed to achieve the RF match is lengthened to an even greater extent.
Also, when the shielding blades that are heated are used for a long time, a silver film coated on the surfaces of the shielding blades can be transformed into a carbon film, which deteriorates the ability of the shielding blades to shield the magnetic field of the fixed coil. To reduce the drop in shield efficiency of the shielding blades due to the heat, there is proposed a method of forming the fixed coil by using a material having a low heat loss characteristic. However, in this case, there is a problem in that the inductance of the material is relatively small, and thereby RF match efficiency is deteriorated.
The present invention is therefore directed to providing an improved RF matching apparatus which substantially overcomes one or more of the problems due to the limitations and disadvantages of the related art.
It is an object of the present invention to provide an improved RF matching apparatus having an inductor which generates relatively small heat, has a long life, and prevents arcs from being generated.
It is another object of the present invention to provide an improved variable inductor which facilitates variable control, and which is adaptable for use in high frequency and high power applications.
These and other objects are provided, according to the present invention, by an apparatus for matching the impedance of an RF generator to the impedance of an RF load for use in manufacturing semiconductor devices by using a plasma, comprising a variable inductor coupled to a variable capacitor and an invariable capacitor. The variable inductor having two inductors coupled electrically with each other and disposed adjacent to each other. At least one of the two inductors is disposed movably to make the magnetic flux of the one inductor interfere with the magnetic flux of the other inductor, thereby to control the inductance of the variable inductor.
According to an RF matching apparatus of one embodiment of the present invention, the two inductors include a fixed inductor formed of an oval and spiral shaped coil having a given number of coil turns, and a rotating inductor formed of an oval and spiral shaped coil having a given number of coil turns and disposed rotatably at the magnetic flux of the fixed inductor. The inner diameter of the fixed inductor is larger than the outer diameter of the rotating inductor. The rotating inductor is rotatably disposed upward or downward from the fixed inductor, or the rotating inductor may be disposed in the fixed inductor. Alternatively, the inner diameter of the rotating inductor may be larger than the outer diameter of the fixed inductor, whereby the fixed inductor is disposed in the rotating inductor. The combined magnetic flux of the fixed and rotating inductors is increased or decreased according to a rotated angle of the rotating inductor.
Each of the coils may be formed of a conductive pipe and a plurality of conducting wires disposed in the conductive pipe. Also, the conductive pipe may be formed of conductive material, for example copper (Cu) or aluminum (Al). A surface of the conductive pipe may be coated with gold or silver having good conductivity. Alternatively, each of the coils can be formed of a single conductive wire having the same diameter as the conductive pipe.
The RF matching apparatus of one embodiment of the present invention further includes a transfer unit that moves the rotating inductor toward and away from the fixed inductor. Accordingly, overlapping width between the fixed and rotating inductors may be increased, so that the inductance value of the variable inductor may be controlled at a greater width.
Also, the RF matching apparatus of one embodiment of the present invention includes a fixing unit that fixes coil turns of the coils in a spaced-apart relation to one another. The fixing unit includes xe2x80x98Exe2x80x99 shaped rings disposed at regular intervals between the coil turns of the coils. Each of the xe2x80x98Exe2x80x99 shaped rings is designed to have a minimized capacity to thereby not have influence on the magnetic field generated by the rotating and fixed inductors.
Also, the RF matching apparatus of one embodiment of the present invention includes connection members at connecting portions between the coils, or between the coils and the capacitors. Each connection member is composed of a gripper having semi-arc shaped gripping portions, and a locking member for fastening the gripping portions.
According to an RF matching apparatus of another embodiment of the present invention, the two inductors include a band type rectangle and whirl shaped fixed coil, and a band type rectangle and whirl shaped rotating coil having a rotating axis penetrating the fixed coil. An output end of the fixed coil is coupled electrically with an input end of the rotating coil. An input end of the fixed coil and an output end of the rotating coil are coupled electrically with the output end of the variable capacitor and the input end of the invariable capacitor, respectively. The combined magnetic flux of the fixed and rotating coils is increased or decreased according to a rotated angle of the rotating coil.
According to an RF matching apparatus of another embodiment of the present invention, the two inductors include a band type rectangle and whirl shaped fixed coil, and a band type rectangle and whirl shaped moving coil disposed movably in parallel to the fixed coil. The fixed and moving coils are positioned to be spaced apart from each other and opposite with respect to each other. An output end of the fixed coil is coupled electrically with an input end of the moving coil. An input end of the fixed coil and an output end of the moving coil are coupled electrically with the output end of the variable capacitor and the input end of the invariable capacitor, respectively. The combined magnetic flux of the fixed and moving coils is varied according to overlapping width between the fixed and moving coils controlled by moving the moving coil.
According to an RF matching apparatus of another embodiment of the present invention, the two inductors are a circular and spiral shaped fixed coil having a given number of coil turns, and a circular and spiral shaped moving coil disposed from the fixed coil upward to be moved up and down, thereby to be overlapped with or separated from the fixed coil having a given number of coil turns. The coil turns of the fixed coil are formed to have winding width enough to be interspersed between each pair of coil turns of the moving coil. An output end of the fixed coil is coupled electrically with an input end of the moving coil. An input end of the fixed coil and an output end of the moving coil are coupled electrically with the output end of the variable capacitor and the input end of the invariable capacitor, respectively. The combined magnetic flux of the fixed and moving coils is varied according to overlapping width between the fixed and moving coils controlled by moving the moving coil up and down.
According to an RF matching apparatus of another embodiment of the present invention, the RF matching apparatus comprises a variable inductor having a band type rectangle and whirl shaped fixed coil, and a rectangle shaped magnetic shield rotating plate disposed in the fixed coil and having a rotating axis penetrating the fixed coil. Input and output ends of the fixed coil are coupled electrically with the output end of the variable capacitor and the input end of the invariable capacitor, respectively. The magnetic flux of the variable inductor is varied according to a rotated angle of the magnetic shield rotating plate.
According to an RF matching apparatus of another embodiment of the present invention, the RF matching apparatus comprises a variable inductor having a circular and spiral shaped fixed coil having a given number of coil turns, and a circular shaped magnetic shield rotating plate disposed rotatably at the magnetic flux of the fixed coil and having rotating axes formed on both sides thereof Input and output ends of the fixed coil are coupled electrically with the output end of the variable capacitor and the input end of the invariable capacitor, respectively. The magnetic flux of the variable inductor is varied according to a rotated angle of the magnetic shield rotating plate.
According to an RF matching apparatus of another embodiment of the present invention, the RF matching apparatus comprises a variable inductor having a circular and spiral shaped variable coil, a mounting plate for mounting the variable coil, and a moving bar for adjusting the length of the variable coil and being fixed to one end of the variable coil through the center of the mounting plate and the variable coil. The other end of the variable coil is fixed to the mounting plate. Both ends of the variable coil are coupled electrically with the terminal of the variable capacitor and the input end of the invariable capacitor, respectively. The magnetic flux of the variable inductor is varied according to a length of the variable coil controlled by moving the moving bar.
As described above, the apparatus of the present invention can vary the magnetic flux, i.e., the inductance of the variable inductor by changing relative position, for example the relative angle or the relative distance between two coils or between a coil and a magnetic shield plate forming a variable inductor. Also, the apparatus of the present invention can vary the magnetic flux of the variable inductor by changing length of a magnetic coil with a given number of coil turns forming a variable inductor.
Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.